The effectiveness of germicidal ultraviolet (UV-C) irradiation as a powerful disinfecting technology has been well documented in peer-reviewed literature as well as in practice. Germicidal UV-C disinfection has been used for decades in disinfecting municipal drinking water, waste water, and in air and surface applications to disinfect against various micro-organisms such as bacteria, virus and mold. UVC devices employ one or more lamps emitting a spectral wavelength output of approximately 254 nm which disrupts the DNA structure of the micro-organisms, rendering them harmless and unable to reproduce.
The lamps typically used in these devices are low pressure mercury vapor discharge lamps. There are three basic types of low pressure ultraviolet lamps in commercial use. A standard output lamp, with input of approximately 425 milliamps has been used for many years. For about two decades, a higher output type lamp with an input of about 850 milliamps has been utilized. Recently a very high output lamp with an input current of from 2.0 to as high as 8.0 amps has become popular in some types of disinfection application. Applications of this type of lamp are popular where high levels of UVC are required such as in municipal water treatment plants.
Construction of the lamp and the materials used are somewhat different to accommodate the high temperatures. With the standard and high output lamps, pure mercury is generally used in the lamp to generate the UVC wavelength of approximately 254 nm. In the very high output lamp, generally the mercury is supplied in an amalgam of metals and may be located on one or more spots placed on the inside of the lamp envelope.
The necessary relatively high doses of ultraviolet radiation typically required to achieve desired disinfection levels requires the use of multiple germicidal lamps. The use of multiple germicidal lamps increases expenses, as well as maintenance. Therefore, it is desirable to use fewer very high output germicidal lamps.
However, applying a very high output germicidal lamp, particularly in air, is not without difficulties. During operation of a low pressure mercury vapor discharge lamp, the vapor pressure of the mercury greatly affects lamp output. For an efficient operation of the lamp, a predetermined range of the mercury vapor pressure inside the discharge vessel is required.
By using an amalgam containing mercury, the mercury vapor pressure can be controlled within this predetermined range for a relatively broad temperature range, allowing operating the lamp at a high efficiency and to deliver a relatively high radiation output within this temperature range. Very high output amalgam lamps thus provide the highest UVC output amongst low pressure mercury lamps and are therefore highly desirable for use for disinfection applications.
The mercury or amalgam of mercury may be located in many different places. In many lamps, it is typically located in one or more locations of the glass inner surface facing the discharge space of the low-pressure mercury vapor discharge lamp. As a result, the amalgam is exposed directly to the discharge space so that the temperature of the amalgam can increase relatively rapidly after the discharge lamp is turned on or lit up. The ideal operating temperature range for germicidal amalgam lamps can vary due to the composition of the amalgam. Typically, it is from 80 degrees C. to 140 degrees C. However, the higher temperatures occurring at high loading of the lamp may cause the temperature of the amalgam to exceed the maximum operating temperature. This high temperature is not generally a problem when very high output lamps are used for water treatment. In this application, the lamps are generally housed in a quartz sleeve and submerged in moving water, which allows cooling of the lamp and maintains the temperature within the proper temperature range. This is most likely the reason that most applications of very high output lamps are limited to water treatment applications only.
Currently, there are little or no applications of very high output lamps in ambient air. In this air application, the temperature at the amalgam spot can exceed 150 degrees C. If the amalgam melts, several things may happen. The amalgam may move out of position and could make contact with an electrode and cause possible shorting or ineffective operation of the lamp. The molten amalgam material may be spread throughout the lamp and solidify at those positions when the operating conditions change. Solidified amalgam material at a position within the discharge path, for example, may become too hot at a later stage of the lamp use, i.e. the amalgam temperature will become outside its temperature range. When the amalgam is operating outside its ideal temperature range, this results in too high a mercury vapor pressure and hence reduces the lamp efficiency.
The positioning of the (germicidal) lamp, i.e. horizontal versus vertical positioning of the lamp, also influences the temperature of the amalgam. If the system design and application do not allow the amalgam to get into their proper operating temperature range, the lamp will have very low UV output and tend to be quite unstable.
Amalgam lamps provide the highest UVC output amongst low pressure mercury lamps and are therefore highly desirable for use in disinfection applications. However, due to the susceptibility of the amalgam to melt when the temperature exceeds the operating range, the use of germicidal amalgam lamps has been almost exclusively limited to water or liquid disinfection applications, wherein the amalgam lamps are constantly submerged in water or liquids, allowing the lamps to operate in the ideal temperature range.
It is the purpose of this invention to solve these temperature problems for air and surface disinfection applications.